Internally finned condenser tube



Sept. 20, 1966 H. HEEREN 3,273,599

INTERNALLY FINNED CONDENSER TUBE Filed Nov. 4, 1964 INVENTOR Hermann Heer'en BY W A ORNEY United States Patent many Filed Nov. 4, 1964, Ser. No. 408,975 Claims priority, application sgrmany, Nov. 9, 1963, 58

1 Claim. oi. 13838) This invention relates to Water-cooled tubes such as used in heat exchangers for condensing saturated steam. In particular, the invention relates to tubes having longitudinally extending internal fins. The tubes of this in vention are also suitable for use in equipment operated with fluids having different heat transfer characteristics.

Exhaust steam, such as coming from steam turbines, is conventionally condensed in surface condensers having a plurality of water carrying tubes which are surrounded by the saturated steam being condensed. The exhaust steam is preferably condensed to as low a pressure as possible so as to enhance the efliciency of the turbo-generator units. The steam pressure in the condenser is largely dependent upon the heat transfer through the walls of the tubes, as well as being affected by the temperature of the cooling water, the velocity of the cooling water flow through the tubes, and the area of the heat exchange surface. The temperature gradient from the steam side to the water side of the tube, as well as the thermal conductivity of the tube material, is used to determine the heat transfer coeflicient, it being noted that, due to the fact that the heat transfer temperature on the steam side of the tube is a multiple of the heat transfer temperature on the water side of the tube, and also that the thermal conductivity of the tube material is of little consequence due to the small thickness of the wall of the tube, it follows that an increased tube surface area on the side of the tube having the lesser heat transfer temperature, which is the inside or water side of the cooling tube, tends to improve the heat transfer coeflicient provided that a suitable tube shape is used and further provided that, where raw water is used as the cooling medium, special attention is paid to keeping the tube clean so that the advantage of having an increased tube surface area is not nullified by a more rapid fouling of the tube than with tubes having smooth inner walls.

Increased surface area tubes have been used which are composed of a brass tube into which is brazed an inner corrugated tube. However, these tubes are largely unsuitable for condensers operating with raw water inasmuch as they are liable to corrode and rapidly foul, and further complicate the means for cleaning. Moreover, they have unfavorable heat transfer characteristics.

The object of this invention is to produce a cooling tube for condensers which avoids the above-mentioned disadvantages and which maintains favorable hydraulic conditions with respect to the resistance to the flow of water through the tube while permitting maximum heat transfer and which is easy to manufacture.

In general, according to this invention, the distance between the tips of adjacent fins is selected so that the viscous shearing force between the water freely flowing through the tube and the water flowing through the grooves between the fins is suflicient to pull the water flowing in the grooves along with and at approximately the same velocity as the water freely flowing through the tube, despite the friction between the water flowing in the grooves and the surfaces of the grooves. Preferably the bottoms of the grooves are in the form of a circular arc. Alternately, the bottoms can have a curved shape simulat- 3,273,599 Patented Sept. 20, 1966 ing a circular arc. Furthermore, the clear distance between the tips of two adjacent fins at which the shearing plane exists between the freely flowing water and the groove flowing water is in length equal to about the total depth of each groove plus the thickness of the tube wall. An optimum shape for the fins for obtaining both good water flow and heat transfer conditions is obtained by forming the sides of the fins in the form of tangents extending from the circular arc bottoms to the fin tips.

The means by which the objects of the invention are obtained are described more fully with reference to the accompanying drawings in which:

FIGURE 1 is a cross-sectional view through a tube according to this invention; and

FIGURE 2 is an enlarged view of a detailed portion of FIGURE 1.

As shown in FIGURE 1, the tube 1 has longitudinally extending internal fins 2 projecting inwardly from a generally cylindrical tubular body having a minimum wall thickness 3.

As shown in FIGURE 2, the bottom a of each groove between adjacent fins 2 is in the shape of a circular arc having the radius r. The clear distance b is between the tips of adjacent fins and the depth h of each groove is measured from this distance line to the lowest point in the bottom a. The sides 0 of the fins are completed by divergent tangents extending from the tops of the bottoms a to the tips of the fins. The cross-section of the fins and grooves is preferably selected in accordance with the following expression:

The lined area x, is the area containing the viscous shearing forces in which the velocity of the water varies due to the internal fluid friction between the water freely flowing through the tube and the water flowing in the groove which depends on the shape of the bottom a between two adjacent fins. The above conditions given for example for saturated steam and water apply also to other fluids upon taking in consideration their specific characteristics. However, it is noted that, in order to obtain optimum results, the increased surface area such as given by the fins should always be on the side of the tube having the lower temperature.

The fins and groove shape according to this invention results in that the water freely flowing through the tube will pull the water flowing through the grooves at approximately the same velocity as the freely flowing water despite the frictional resistance given by the increased water-exposed surface area of the grooves.

Having now described the means by which the objects of the invention are obtained, I claim:

A water-cooled tube for a heat exchanger such as for condensing saturated steam comprising a tubular body having a generally cylindrical inner wall, a plurality of fins extending longitudinally of said body and projecting from said wall toward the interior of said body with grooves having circular arc bottoms lying between adjacent fins, and the distance b between the tips of adjacent fins and lying within the range of the line x of the interior water friction between adjacent fins is larger than the height h of line b above the lowest point in bottom a formed of an are having a radius r, in which 3 4 and straight sides for said grooves composed as tangents References Cited by the Examiner divergently extending from the circular arc bottoms to the FOREIGN PATENTS tips of the fins, the tubular body being such that water freely flowing through the center of said body Will pull the 1327402 4/1963 France' r 852,544 1/ 1953 Germany. water flowing through said grooves substantially at the v 2 464 1892 Great Britain.

velocity of the freely flowing water despite the frictional resistance on the Water in the grooves caused by the water- LAVERNE GEIGER Prmary Exammer' exposed surfaces in said grooves. C. HOUCK, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N06 3,273,599 September 20, 1966 Hermann Heeren It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, lines 51 to 34, for that portion of the formula reading b read b Signed and sealed this 22nd day of August 1967.

(SEAL) Attest:

ERNEST W. SWIDER Attesting Officer EDWARD J. BRENNER Commissioner of Patents 

